Printing telegraph system



March 1, 1955 H. c. A. VAN DUUREN 2,703,361

PRINTING TELEGRAPH SYSTEM Filed June a, 1949 4 Shets-Sheet 1 F I G. l

RADIO TRANSMITTER APPARATUS KEYING TRANS" I TTE R DISTRIBUTOR (TD) RADIO TRANSMITTER INVENTOR. HENDRIK 6ORNE| .IS ANTHONY vanDUUREN BYM 4 ATTYS.

March 1, 1955 H. c. A. VANDUUREN 2,703,361

PRINTING TELEGRAPH SYSTEM Filed June 8, 1949 4 Sheets-Sheet 2 FIG. 2

RADIO RECEIVER APPARATUS RECEIVING DISTRIRJTOR (RD) INVENTOR. HENDRIK CORNELIS ANTHONY vonDUUREN ATT Y8. v

March 1, 1955 H. c. A. VAN DUUREN' PRINTING TELEGRAPH SYSTEM 4 Sheets-Sheet 3' Filed June 8, 1949 F I G. 3 comscrms APPARATUS (cm V||+o+0+oo+ INVENTOR. HENDRIX connsusmmouv vcm DULREN ATTYS.

March 1, 1955 Filed June 8, 1949 H. c. A. VAN DUUREN 2,703,361

PRINTING TELEGRAPH SYSTEM 4 Sheets-Sheet 4 FIGS | 2 34 5 s 78 9:0 |2|3|4|s|s 3 lsrum 4 FIGS I 9| 92 93 94 95 96 97 98 99 I00 I02 I04 I06 I08 .L

IOI I03 05 I07 INVENTOR.

HENDRIK CORNEUS ANTHONY vanDULREN United States Patent PRINTING TELEGRAPH SYSTEM Hendrik Cornelis Anthony van Duuren, Wassenaar, Netherlands, assignor to Staatsbedrijf Der Posterijen, Telegrafie en Telefonie, The Hague, Netherlands Application June 8, 1949, Serial No. 97,199 Claims priority, application Great Britain June 8, 1948 6 Claims. (Cl. 250-8) The present invention relates to printing telegraph systems, and is concerned particularly with improvements over the embodiment of printing telegraph system disclosed in the Patents 2,279,353 and 2,313,980 issued to me on April 14, 1942, and March 16, 1943, respectively.

In all applications, the invention is primarily concerned with the troubles arising in these systems from transmission disturbances. Transmission disturbances are particularly present in radio transmission where static and fading frequently mutilate the signals. For this reason, the invention has its primary field of utility in connection with radio transmission, but it will be understood that the invention can also be, employed in wire transmission sys tems over land and cable lines for avoiding ditficulties arising from atmospheric disturbances, induction from adjacent power lines, etc.

The present invention is in the nature of an improvement on the prior specification in that of the two warning signals VI and VII, only one. such signal is retained, and is operatively transmitted only once per mutilation cycle.

Specifically in the prior disclosures of the aforementinned types, the equipment at a station B was, operative responsive to receipt of a mutilated signal from a station.

A to effect the blocking of its receiver BR for an. interval equivalent to the receipt of six signals and the transmission of a warning signal VI by its transmitter BT to the first one of the stat-ions A to ettect the stopping, of the transmitter equipment AT thereat and theretransmission of the portion of the original signal which was mutilated.

in the event that signal.Vlis-mutilatedin its transmis-. sion by BR, the receiver AR atstation Ahas nom'eans of distinguishing this signal. from. an. ordinary letter which is mutilated, and accordingly it has, no other choicethan to demand a repeated transmission of signal VI. Station.

A sends a warning. signal to, the receiver. at. station B and receiver AR at station .A is blocked six signals. Since this demand is effected in the samev manner as just described, a further delay is experienced during the repetition of the warning signal.

An auxiliary signal VII is necessarily sent in thiseinbodiment to assure the issue of a second signal'VI by the transmitter ET in the event that the. first signal Blwas mutilated on arrival.

If'th'is precaution were not taken the transmitter BT atstation B would be out of step bysix signals.

Assuming the second warningsignal is not mutilated, it.

the same manner when receiving either a warning signal.

correctly, a warning signal mutilated, or an ordinary signal mutilated. in each case the receiver blocks itself for a six unit time period and commands the sender to issue a uniform warning signal followed by a repetition-cycle of the garbled portions.

The improved and novel arrangement of the equipment of the present invention effects the elimination of "the serious delay which is possible in known arrangementsby minimizing the number of signals required to elfect thedesired signalled retransmission. Additionally, the re for. an intervalof duced number of control signals required for such purpose in the disclosed embodiment minimizes the possibility of confusion between the control of the stations whereby a reliable operating arrangement is effected.

:The invention disclosed in the present application and in my prior patents provide a system in which the transmitted signal elements are made mutually protective by having them comprise impulses having different electrical values which are so chosen as to produce a constant ratio or constant total electrical value for each transmitted signal. Any deviation from this constant relationship in the signals received at the receiving station is an indication that the signal has been mutilated in transit from one station to the other, calling for a retransmission of that signal. In the preferred embodiment of the invention, the desired constant relationship is obtained by having the signals consist of a given number of positive and negative signal elements, which are transmitted in a combination characteristic of each signal. The mutually protective relation is preferably obtained by causing the proportion of positive and negative elements to be identical in each signal. The occurrence of a parasitic impulse or of fading during the transmission of the signal is detected through the deviation from normal of the proportion of positive and negative elements as determined at the receiver. Upon the reception of such a mutilated signal in the normal course of transmission from station A to station B, receiving station B emits a warning signal which is transmitted to transmitting station A for indicating that such mutilation of a signal has occurred. The warning is effected by the transmission of a number of warning signals not belonging to the group of normal communication signals. The reception of these warning signals at the transmitting station which has been transmitting the normal communication signals, sets into operation certain corrective apparatus at that transmitting station which performs certain corrective functions such as stopping the keyer, then stepping back the perforated strip in the kcyer and finally restarting the transmitter. This will be referred to in a greater detail later.

If it were attempted to employ the normal five unit code, represented by the Baudot code, in the application of the above idea, a shortage of different combinations would'result, because when operating upon the basis of a given proportion or ratio of positive and negative elements there would be several combinations of such five unit code which obviously could not satisfy the requirements relating to this proportion or ratio. It is therefore desirable to employ a code in which the signals are made up of a greater number than five units or elements.

In the preferred embodiments of the inventions disclosed in this application and in my prior application, I employ a code containing eight units or elements. The eight unit code is particularly suitable for the practice of the invention in that when the code is obtained by conversion from the five unit code which is usually employed in mechanical telegraphs or landlines, thirty of the thirty two combinations of the five unit code may be changed into eight unit code signals by simply adding three elements, of which three, two, one, or none are marking units. Only those signals of the five unit codes which have five identical units have to be transformed in a difierent manner.

The preferred embodiment of the invention, as it will be hereinafter described, uses a transmitter which transmits with an eight unit code, in response to received signals which are formed on the basis of a five unit code. The transmitter includes transforming apparatus for transforming the five unit signals into eight unit signals. Similarly, this embodiment utilizes a receiver which receives the'eight unit code and which receiver includes transforming apparatus which retransforms the received eight unit'signals into five unit signals for controlling a printer. it will be clear that this transforming apparatus is not essential to the application of the fundamentals of my invention. For example in situations where messages originate directly at the transmitting station, or in situations where messages received over a landwire ina five unit code (such as the Baudot code) are printed at the" transmitting station and are then manually recast into a code having a different number of units. There v is no necessity of employing such transforming apparatus. However in view of the fact that in the most instances the large bulk of messages will be conveyed over landlines to the radio transmitting stations, and in view of the fact that these landlines are usually equipped to work with a five unit code, it is desirable to provide the aforesaid transforming apparatus to transform the five unit code into the eight unit code at the transmit ting station, and to transform the eight unit code back into the five unit code at the receiving station. In this regard, it is to be understood that the description of an eight unit system is not to be interpreted as a limitation of the invention, since seven units suffice for obtaining the required number of combinations; provided that in each signal four and three equal signals elements should always occur, in which case seven units provide,

( 35 combinations However the uses of eight units is more advantageous since it appears to simplify the apparatus considerably, as in this case all signals from the five unit code, except those having five equal elements, may be used in the eight unit code by merely completing these signals to eight unit signals through the addition of three elements.

Referring now to the correcting apparatus or fault clearing apparatus which is set into operation whenever a transmitted signal is mutilated in its transmission from one station to another, such apparatus is provided at each station and is arranged to respond to the reception of such a mutilated signal at a receiving station by immediately bringing about the emission of warning or-correcting signals from said receiving station, which signals are transmitted back to the transmitting station for effecting a necessary retransmission, of the mutilated signal. The reception of the warning signal at the transmitting station performs the corrective functions of stopping the keyer, then stepping back the perforated strip in the keyer, and finally restarting the transmitter after a predetermined time. Inasmuch as the eight unit code, when limited only to the condition that each signal shall comprise four positive and four negative elements, affords seventy distinct signal combinations, it will be evident that a large number of signals will be available for use as Warning signals. In the system of my invention, a limited number of signals (i. e. two or three, depending on the transmission time) is repeated whenever a disturbance occurs.

In the present application I have shown improved correcting apparatus or fault clearing apparatus which is a substantial departure from the embodiment of my prior application.

Summarizing the duties required to be performed at each station, it will be seen from the foregoing that in the transmission of normal communication signals from station A to station B, the transmitter at station A has to first take the five unit signals (which usually stand ready at the transmitting station in the form of a perforated paper tape) and convert or transform these signals into balanced eight unit signals, and to then transmit these balanced eight unit signals over the radio path. Furthermore, transmitter A must be capable of transmitting warning or correcting signals to station B for the purpose of warning transmitter B of disturbances on the path B-A (i. e., whenever signals which have been transmitted back from transmitter B along the path B-A have been mutilated in transmission).

With reference to receiver B, this receiver has to convert the eight unit signals arriving on the radio path into five unit signals, which conversion or transformation consists in the simple admission of the first five of the elements of the signal as received to a five unit printer. except in the cases in which the original signal contained five identical elements, or where it was a signal for indicating a disturbance on the path B-A. With reference to Figure 8 of the aforementioned patent and Figure 8 of the present disclosure, it is apparent that the operation of the two systems responsive to the detection of amutilated signal in an incoming message is somewhat similar in nature. The example as there shown assumes that the message A, B, C is being transmitted by ET (the transmitter at the second station to AR the receiver at the first station), the message a, b, c is being transmitted from AT (transmitter at first station) to BR (receiver at the second station),

and that the letter 11 of the message is mutilated in transmission (i. e. the message on arrival at ER is comprised of an unequal number of marks and spaces).

In both systems, the testing equipment at station B is operative with detection of the mutilated message to operate associated corrector apparatus which stops the message transmission of its associated transmitter BT and causes same to send a warning signal back to the receiver AR at the first station (the warning signal VI in the previous embodiment and Warning signal VII in the new embodiment). The corrector apparatus simultaneously effects blocking of the receiver BR at the second station for a period equivalent to a six element interval, so that not only the mutilated letter b is rejected but the further letters c, a, etc., which are transmitted by AR at the first station prior to receipt thereby of the notice of message disturbance, are also blocked from the receiver BR at the second station.

As the warning signal (VI in previous embodiment, VII in the new embodiment) arrives at the receiver AR at the first station, the transmitter at the first station will be transmitting the letter e, the transmitter equipment having advanced that far due to the delay in propagation time of the signals over the lines. Accordingly the warning signal detecting equipment intercepts the warn-- ing signal and operates the corrector apparatus thercat to step the tape back over 0 and c to b, so that retransmission of the signal which was mutilated may be effected, and the following signals which were blocked at the distant receiver may again be transmitted. Thus six letters in all must be rejected at the distant receiver BR, these letters being b, c, d, e, d, and c.

It is apparent from the foregoing that the operation of both systems is similar with the mutilation of a letter in a transmitted message. The features of the new and novel system are primarily evidenced in the event that a warning signal is mutilated in its return to the station which transmitted the first message which was mutilated, this being termed in the art as a mutual di turbance.

Referring to Figure 10 of the aforementioned patent, it is noted that if the first warning signal VI is mutilated in its transmission to the first station A, the testing equipment will operate as a result of the unbalance and the warning signal detection equipment will not be operated. As a result the first station A assumes the incoming signal was one of the elements of the incoming message and reacts in such fashion; that is, the first station A has no other choice than to ask for a repetition of the signal, this request being accomplished by the first station A in the same manner as station B requested repetition of the mutilated signal b. The corrector apparatus at station A new causes transmitter AT at station A to transmit the warning signal VI to station E and causes the local receiver AR at the first station A to be blocked for the following six intervals during such request.

After the elapse of six signal intervals the corrector apparatus at the second station B causes the transmitter BT to comply with the request from station A and the warning signal VI is repeated. If the signal is undisturbed at this time, then only is the first station informed that its letter b was originally mutilated.

It is apparent therefrom that in the event of the mutilation of the warning signal, extreme delay is experienced in the signal transmission. Additionally, as a result of this particular system arrangement, it was necessary to provide for an auxiliary signal VI! to insure the issue by the station B of a second warning signal VI whenever the first warning signal VI was mutilated on arrival at the first station A, for without these signals VII the transmitter BT at the second station would reinitiate the transmission of its own message during the period which the receiver AR at the first station is blocked. Thus both extra equipment and extra signals were required to accomplish satisfactory protection in the event that a warning signal was mutilated in the transmission path.

In the arrangement of the present invention, the receivers at each of the stations comprise a testing unit for testing the balance of the signals and a warning signal detection unit for responding to a single incoming warning signal, the testing unit and the warning signal detection unit being connected to operate the corrector apparatus in a common manner whenever either is energized. Thus.- the. corrector apparatus isoperatedt in. a common; manner responsive; to. receipt: of! either;-

(a) a. warning, signal, correctly (b) a warning. signal. mutilated,- or (c) an ordinary signal mutilated;

Specifically, with the receipt of any.. of these signals the corrector apparatus blocks its associated receiver for a time period equivalent: to six signal; intervals,.stops.-the local printer, causes the associated, transmitter. to .issues a. uniform warning signal; immediately: followed? by. a repetition cycle (and not by. a. sequenceof auxiliary warning signals) and backs. up the associated tapea predetermined. number; of steps.

With reference to Figure 8; it is. apparent that thewarning signal. detector unit controls the correcton apparatus at the; firststation, A responsive. to. receiptof the warning. signal from station B; to effect the reversal ofthe tape to bring the element b which was mutilated back into position for retransmission, The equipment operates in such fashion even; if the, warning signal is mutilated in that the testing equipment;,will then be operated by the unbalance and is adjusted to operate the corrector apparatus in the Same; manner; as: the warn: ing signal detector unit.

It is also apparent from Figure 8 that with the; re.- ceipt ofthe warning signal (mutilated or unnrutilated), the corrector apparatusat the, first station A; isoperative to cause the transmitter AT to transmit the Warning. Sign nal VII to station B. However, since; the equipment at the distant station E; is blocked as a result of its own warning signal transmission, the; second warning, signal transmitted in the direction A-.B .is blocked from the receiver at station B and no effect is experienced.

As the tape at the first station, is backed to the. pointwhere the letter which was mutilated. in transmission: is in position (b), the transmitter AT is again rendered operative to retransmit the mutilated. letter b-- and. the-letters following same in the message. The, particular requirements to be satisfied bythe transmitter A and. re ceiver B will be better understood byreferring to the accompanying drawings illustrating one preferredernbodiment of my invention. In these drawings:

Figure 1 is a circuit diagram ofthetransmitter. apparatus of each station;

Figure 2 is a circuit diagram of the receiver apparatus of each station;

Figure 3 is a circuit diagram; of the correcting or fault clearing apparatus which is. associated with the trans; mitting and receiving apparatus. of each station Figure 4 is a chart illustrating different. combinations. available in the eight unit code;

Figure 5 is a. timing diagram of. a group of rotary contactors which are driven by the timing shaft of the transmitter;

Figure 6 is a timing diagram. of a group. of rotary Contactors which are driven by the, timing: shaft of the. receiver, and is also a timing diagram of the start-stop Teletype connected thereto;

Figure 7 is a timing diagram. of a group of rotary contactors which are driven by the timing shaft of the cor.- recting apparatus;

Figure 8 is a diagram or chart represent-in disturbed reception, and showing the timed relation at 'stations A and B between normal. communicationsignals, mutilated communication signals and a warning signal.

The transmitter of Figure 1 can be regarded as the transmitter of station A, or as the transmitter of station B; and, similarly, the, receiver of Figure 2 can heregarded as the receiver of station B, or as the receiver of station A. it will be noted that the correcting apparatus of Figure 3 is enclosed within a dotted rectangle CA, and that in placing this rectangle approximately in registration with the fragmentary portions" thereof illustrated in Figures 1 and 2, the electrical connections between the correcting apparatus and the transmitter andv receiver will be readily apparent.

Referring now to Figure 4: which shows different code combinations in which the eight unit signal is made up, the transmitter A has to satisfy certain requirementswith reference to creating these eight unit: signals. For ex,- ample, the five unit signals which are to. be transmitted from transmitter A and; which have 141- equai elements at most, have to be completed; by.- the, additionof three elements in such a manner that the, resulting eight unit signal contains four. positive and four negative elements. For. accomplishingthis relation, four. combinations of the eight-possible code combinations of the three added elements are required viz., forthe cases in which one, two, three, or four positive elements were present in the original' signal. These four combinations have been shown in Figure 4 at the lines I.IV. In this chart, the signal elements denoted by the circles or zeros may, for convenience of reference, be referred'to as the spacing elerents, and the signal elements denoted by the X marks may be referred to as the marking elements.

For example, in the Baudot code the flat tops in the current waves are commonly referred to as marking elements and the valleys are commonly referred to as spacing elements. correspondingly, in the present disclosure the X marks in Figure 4 may be regarded as the-tops or marking elements, and the circles as the valleys or spacing elements, this arbitrary designation, however, being solely for convenience of reference. Referring more particularly to these socalled normal signals indicated in lines l-l\ line 1 illustrates the three signal elements which are added when the original five unit signal contains only one marking. element; line If the three signal elements which are added when the original signal contains two marking elements; line III the three signal elements which are added when the original signal contains three marking elements; and linelV the three signal elements which are added when the original signal contains four marking elements.

A further requirement of the transmitter is that if the original five unit signal has five equal elements, such signal must be transformed into a balanced eight unit signal comprising equal numbers of positive and negative elements. There are two instances of such a five unit signal, one in which all five elements are. positive (spacing elements 0) and the other in. which all five elements are negative (marking elements X). These two signals are shown in their transformed state in lines 0 and V inv Figure 4, signal 0 being a transformation of the original signal having five. spacing elements 0, and signal V being a transformation of the. original signal having five marking elements X. in contradistinction to my aforementioned copending patents, the last three elements of transformed signal V differ from the last three elements of transformed signalI in the present disclosure. The sequence or order of the last three elements in each of these transformed signals differs, moreover, from each of. the other four sequences or groupings 1, li, HI and IV. As will be hereinafter described, when the receiver receives. either one of the two transformed signals 0 or V it perceives that a transformation has taken place.

The four normal signals l-lV and the two transformed signals 0- and V exhaust six combinations in all; Hence, of the eight possible three-element combinations, two yet remain, and these are used at the transmitter for the emission of a warning signal under control of signalling relays, this signal being shown in line VII in Figure 4. The receiver thus has the particular requirement to select between (1) normal signals, represented at I-IV in Figure 4; (2) transformed signals indicated at O, andV in which the first five elements have to undergo a retransforrnation opposed to the transformation experienced by these elements at the transmitter; and (3) warning signals indicated at VII in Figure 4. Lastly, the receiver B- should be adapted to control its own transmitter B for the emission of a Warning signal to A whenever a disturbance occurs on the path AB. Similarly, in this same regard, the reception of a warning signal at B has to occasion the repetition of the warning signal. previously mutilated on the path BA. The converse of this situation is, of course, true when considering the message signals. transmitted at B for reception at A.

Referring now to Figure l, the transmitter comprises the five contact fingers or feeling tongues 21 to 25, inclusive,

adapted to coact with the perforated paper tape on which the message is recorded in conventional five unit code, this. part of the apparatus being commonly referred to as, a keyer.

When these contact fingers are in their upper positions, which is the case when the tongues register with perfora? tions, they establish engagement with cooperating upper contacts, and when they are in their lower positions they establish engagement with cooperating lower contacts. Different polarities or potentialsv are imposed, on these.

agner contacts to establish the marking or spacing elements of the first five unit portion of the complete eight unit signals. The perforated paper tape is moved in a forward direction when the forward or start magnet S is energized over conductor 142, and the tape is moved in a rearward direction when the backward or reverse magnet T is energized over conductor 143. A common return conductor from both magnets connects through rotary contact $5 with battery midpoint, this rotary contact effecting the intermittent energization of the selected magnet. The two conductors 142 and 143 have connection with the correcting apparatus CA later described in connection with Figure 3. Throughout the circuit diagrams of Figures 1, 2 and 3, all ground connections will be considered as corresponding to a connection to battery midpoint.

The transmitter also comprises any known or preferred form of transmitting distributor TD comprising the eight contact segments 33 to 4t), inclusive. The rotary elements of the distributor connect with the polarized sending relay 75, which in turn connects with any suitable radio transmitter RT which emits the radio wave in which the signal elements are defined in any well known manner. Each station having such radio transmitting apparatus RT also includes as a part of its equipment a suitable radio receiver RRT which will be described later in connection with Figure 2. It will be noted that the five contact fingers 21, 22, 23, 24- and 25 of the tape controlled keyer have permanent electrical connection with the first five distributor segments 33, 34, 35, 36 and 37 of the rotary distributor.

The apparatus for adding the three extra signal elements to make up the eight unit code comprises a bank of three supplementing relays 29, 3t) and 31, it being noted that their respective armatures 26, 2'7 and 28 are connected with the last three segments 38, 39 and it! of the transmitting distributor TD. These relays are of the polarized type in which each armature remains in its actuated position after the cessation of the actuating current impulse and until a current impulse of opposite polarity traverses the relay winding for actuating the armature to the other position, these armatures remaining in rest positions (in engagement with their lower contacts) when negative polarity is applied to the relay windings. When the armatures are in engagement with their lower contact they receive positive polarity, and when they are in engagement with their upper contact they receive negative polarity. The windings of said relays 29, 39 and 31 are connected with the rotary timing contacts 4. 5 and 6, respectively, and also with timing contact 3 and relay 53. The timing contacts 1 to 16, inclusive, are all mounted on a common shaft V for synchronous operation, these contacts only being shown diagrammatically in Figure l but actually having the predetermined timing intervals illustrated in Figure 5. The shaft V rotates with and has the same speed as the rotary member of the transmitting distributor TD, and may be referred to as the transmitter timing shaft.

Referring now to themanner in which the transformed signals and V of Figure 4) are formed, the apparatus for transforming the signals which have five equal ele ments into signals having five non-equal elements, followed by three additional elements in the characteristic combinations illustrated at O or V, comprises a pair of polarized relays 41 and 42 which are adapted to be energized whenever all of the contact fingers or feeling tongues 21-25, inclusive, occupy similar positions. Relay 41 has a bias towards spacing position and relay 42 has a bias towards marking position. The movement of all of said contact fingers 21-25 to similar positions causes these fingers to have potentials of equal polarity. If then, shortly after the fixation of the five unit signals, all of the rotary timing contacts in the group 9 to 13 inclusive are closed, it will be evident that a current of corresponding direction will flow through the polarized relays 41, 42. This current will be of one polarity if all of the contact fingers 21-25 are in their raised positions, and will be of the opposite polarity if all of said contact fingers are in their lowered positions. Accordingly, this current will energize the relays 41 and 42 and cause either one or the other of the armatures 45 or 46 to move to circuit closing positions, depending upon the polarity of the current to said relays. At the moment at which timing contacts 9-13 are closed. the timing contacts 1 and 2 are open (see Figure 5), so that the spacing and marking contacts associated with the contact fingers 21-25 are connected to the voltage source through resistances 43 and 44. It will thus be seen that the closure. of timing contacts 9-13 does not result in a complete short circuit in the event that the contact fingers 21-25 do not occupy similar positions. In such case, the transforming apparatus 41, 42, 48, 49, 50 etc. should not function, and to this end the relays 41 and 42 do not carry current at this time, inasmuch as the contacts 9 to 13, as well as contact 14, then have the potential of battery midpoint.

When the relays 41 and 42 are energized in the operation of transforming a signal, they close holding or lock-up circuits through their armature contacts and 46, such holding circuits being opened upon the opening of timing contact 14; Therefore it will be seen that until the opening of timing contact 14, the point 47 has a potential corresponding in polarity to that of the similarly positioned contact fingers 21 to 25. This voltage, whether of one polarity or the other, now energizes the relay 4%, which attracts its armatures 49, 50, 51 and 52. The nature of the transformation resulting from this energization of the relays 48 will be first described in the situation where a five-space signal is being applied to the contact fingers 21 to 25', in which situation the. contact fingers are all on their lower contacts in Figure 1, such corresponding to five successive circles according to the system of notation shown in Figure 4. After the armatures 49 and have been attracted by the energization of the relay winding 48, contact finger 21 remains connected with positive (such being the spacing current of zeros of Figure 4); contact finger 22 is now connected to negative through the new position of armature 50; contact finger 23 remains connected position, contact finger 24 is now connected to negative through the new position of armature 50; and contact finger 25 remains connected to positive. Thus, the first five elements of signal 0 of Figure 4 are formed. With reference to the last three elements of this signal formed through the supplementing relays 29, 3b and 31, relay 31 is energized on time through timing contact 4. In the process of forming these last three signal elements, the winding of relays 29 is connected with positive polarity through armature 52which has been moved to its actuated position by the energization of relay 48.

The windings of relay 3% is connected with negative through armature 51, which has also been moved to its actuated position by the energization of relay 48. The

" windings of relay 31 is connected to positive if the original signal consisted of five spacing units (0), and is connected to negative polarity if the original signal consisted of five marking units (X). The choice between connecting the winding of relay 31 to positive polarity or to negative polarity is brought about by the action of a bridge circuit and a polarized relay 53 to be described in detail later, this bridge circuit and relay generally having the duty of making the total number of marking units in the final eight unit signal equal to the number of spacing units. When the windings of the three supplementing relays 29, 30 and 31 are thus connected with positive, negative, and positive, respectively, as above described, the armatures of said relays are connected with negative, positive and negative, respectively, thereby producing the last three signal elements shown in signal 0 (Figure 4). When the first two supplementing relays 2 9 and 30 are energized in this same manner but the winding of the last relay 31 is energized with negative polarity instead of positive, through the aforementioned bridge circuit and relay 53, then the armatures of the three relays produce the last three signal elements shown in signal V (Figure 4). The manner in which the five marking units of the original signal are transformed. into the first five signal elements of signal V willbe apparent from the description of the preceding transformation in the case of signal 0. it will be noted that in transforming the five marking unit signal into signal V,- the contact fingers 2125 are all in their upper positions, and hence the shifting of relay arma tures 49 and 50 does not influence the polarity impressed on contact fingers 21, 23 and 2S.

' Referring now to the manner in which the normal signals (l-'lV of Figure 3) are formed, the three control relays 41, 42 and 46 remain at rest whenever a signal having four identical elements or less than four identical elements is applied to the contact fingers 21-25. The three signal supplementing relays 29, 3t) and 31 return to rest position in engagement with their positive contacts when negative polarity is applied to the windings of" these relays over the circuits closedby the rotary contacts 3, 4, and 6'. Under such conditions, these supplementing relays thus add spacing elements ('0) to the five units of the original signal. In this manner, a signal having four marking units and one spacing unit is. converted into the eight unit signal IV of Figure 4. Inthe case of a signal in which the number of marking units is smaller than four, the polarized relay 53 is energized in abridge connecting with the resistances 54-61 by way of' the test conductor 32. This test conductor will not carry current when the eight unit signal is balanced, because such causes equal amounts of positive and negative currents to flow in the resistances 54-61. In order to effect the conversion of the diiferent normal signals, the five unit signal is tested three times by the action of timing contacts 4, 5, 6 and 7. If it is not balanced the first time, relay 30 is energized by way of rotary contact 5 and armature contact 62 of relay 53, the armature. of relay 30 being thereby moved to its upper position for transmitting a marking unit to the rotary distributor. If at the second test the signal is not yet balanced, the lower supplementingrelay- 31 is energized, thereby moving its armature into marking position. Finally; if the signal should not yet be balanced at the third test, the upper supplementing relay 29- is energized for moving its armature into marking position.

In this manner, the signals III, II,'and I of Figure 4 are consecutively formed. respectively from original signals having three, two, or one marking units.

In the above functioning of the timing contacts 4, 5, 6 and 7, it will be seen that for causing the aforementioned testing operations the rotary contact means 7 compl'etes the circuit of the relay 53 three times, and that during these closed circuit intervals the. contacts 5, 4 and 6 successively energize the windings of relaysv 30, 31 and 29 in that sequence.

Referring now to the manner in which the warning or correctingsignal VII of Figure 4 is formed, it will be seen that the signals 0 to V, inclusive, utilize groupings or sequences of the three added elements different from that shown in the last signal VII.

This last signal is used as warning signal, but it is necessarythat it be completed by five preceding elements of such polarity that a balanced eight unit signal results. Said warning signal is created by the energization of the winding of the relay S2. over conductor 144, which connects through timing contact 16 with the corrective apparatus CA, as will be later described in. connection with Figure 3.

The other end of the relay windings is connected through rotary contact with battery midpoint. Upon energization, relay S2 is adapted to be locked-up through an armature and a front contact connected with negative polarity, this locked-up relation being maintained until the opening of rotary contact 15.

The energization of warning signal relay Sjz actuates armatures 76,, 7-1, '72 and 73, and thereby formulates the warning signal VII. Movement of armature. 70 to. its right hand position results in positive polarity being placed on contact fingers 22 and 24, irrespective of whether these fingers are in their upper or lower positions. Movement of armature 71 into, its right hand position results. in negative polarity being placed upon contact imgers 21, 23. and 25, irrespective of whether these fingers. are in their upper or lower positions. The movements of armatures 72 and 73 into their right hand positions. effects a transposition with respect to the supplernenting relays and. 31 so that the last three elements of warning signal VII consists of two spacing elements and a marking element, in that order. When this warning signal VII is received at a particular station, it exertsv a control influence on the correcting apparatus CA of that station similar to the influence exerted bythe reception of a mutilated signal. This will be described more in. detail later in connection with Figure 3.

Referring now to the receiving apparatus illustrated in Figure 2, it will be noted that this apparatus. comprises any suitable radio receiver RR. which communicates the received signals to a polarized receiving. relay 7.6. As Previously described, each station, having such radio receiving apparatus RR also includes. as a part of its equipment a suitable radio transmitting apparatus RT, illustrated in Figure 1. Such radio receivers and transmitters,

are. not shown, in detail as. they may be of any conventional, well known design. The receiving relay 76 en- 1 0 ergizes the rotary receiving; distributor R13)- with different polarities corresponding to the positions consecutively occupied by the armature of the polarized" sending relay 75 (Figure 1). The receiving apparatus also comprises amultiplicity of rotating timing contacts 91 to 108, inclusive, all mounted on a rotating shaft V Shaft V rotates with and has the same speed as the rotary member of the receiving distributor RD, and the timed relation of these several contacts is illustrated in Figure 6. Figure 6 also affords a timing diagram of the start-stop teletype connected with the receiver. The receiving distributor RD is shown with sixteen contact segments, the first thirteen of which connect with the windings of the polarized relays 77' to 89, inclusive. The fourteenth, fifteenth, and sixteenth segments are connected back to the windings of relays 82, 83- and 84. The first eight relays 77 to 84, inclusive, are energized in conformity with a received eight unit signal (which, for clarity of description may be referred to as the first received signal). The last five relays 85 to 89, inclusive, together with the last three relays 82, 83 and 84' of the first group of eight, serve for the, reception of the next eightunitj signal (which may be referred to as the second or next signal to be received). The relays 77-89 are of the polarized type in which, after the, cessation of current flow through the relay windings, the armatures remain in the positions last assumed. Thirty of the utilized thirty-five combinations of the eight unit code (exclud-. ing signals 0, V, and VII of Figure 4) are received in the following manner. Upon the arrival of one of these thirty combinations, the first five elements of the firstn'ientioned signal are received by the relays 77 to S1, and are directed to the printer without any modification. This is effected at suitable moments; through timing contacts 94 to 98, and occurs for all signals except those in which the three element combination received on the last three relays 82', 83 and 84 of the first group. correspond to the last three elements of signals 0, V and VII.

When the signal terminateswith the last three elements of the letter combinations, the armatures of relays 82, 83 and 84', and consequently the armatures 117-121 of relays 111, 112, and 113 are causedto occupy such positions that one of the relays 1:14, M116. is energized via circuit connections established through armatures 117-121. Relay 114 is energized on the arrival of signal 0, the resulting actuation of the armature of said relay interrupting the printer start: circuit which extends through rotary timing contact 104 and through said relay armature, and thence byway of conductor 141 to the correcting apparatus CA. Relays 115 and 116 are energized upon the arrival of a combination,corresponding to signal V. Relay 115 actuates armature 122 which is effective to impress negative polarity on all of the lower contacts of the second series of five relays 85-89. Relay 116 actuates an armature. 123, which is likewise effective to impress negative polarity on all. of the lower contacts of the first group of five relays 77-81. These two transforming relays 115 and 116 are each provided with lock-up armatures which are connected to, negative polarities through the rotary timing contact 105. After the operation and locking of relays 115 and 116, relays 82-83% and their connected relays 111-113 are again free to be controlled anew by the next signal, which is done when the first five elements of this next signal have been registered on the relays 85-89. To this end, it will be noted that the armatures of the relays 85-89 are periodically connected to the printer by way of the rotary timing contacts 99-163. The rotary timing contacts 106-187, which are interposed in the circuits of the transforming relays 115 and 116, are so timed that the first mentioned signal which is registered on relays 77 to 81 is adapted to.

influence relay 115, while the next received signal rcgistered on relays 85 to 89 is adapted to influence the other relay 116.

Upon the energization. of relay 115 and the resulting actuation of armature 122, negative polarity is transmitted to the marking and spacing contacts of relays 85-89 so that the first elements. of the transformed signal registered on these relays undergo a conversion or retransformation opposite to that which has been applied to them at the transmitter.

Re y 116 s nerg zed. in. c rre ponding; manner by the first mentioned signal. received on the. relays 77-81, and the actuation of' the armature 123 of this relay also transmits negative polarity in such manner that the marking and sapcing contacts of these relays 77-$1 receive negative polarity, whereby the first five elements registered on these relays undergo a conversion or transformation opposite to that has been applied to them at the transmitter.

Upon the reception of warning signal Vll, negative polarity is impressed upon conductor 125 from these same relays and their associated armatures. The conductor 125 is connected to initiate the operation of the correcting apparatus CA, as will be later described in connection with Figure 3.

I shall now describe that portion of the receiving apparatus which detects the signals which have been mutilated by atmospheric disturbances or otherwise. The aforementioned first received signal is elfective to energize relays 7784, and the armatures of these relays are then connected in circuit with the testing relay ST by way of timing contacts 92 and 93 through the resistors 126-133.

The upper and lower contacts of relays 77-fi9 are connected either to marking voltage (negative battery) or to ground (battery midpoint), and accordingly, the other extremity of the winding of relay ST is connected to a point 139 which has a potential equal to half the said voltage. If the signal which has arrived contains equal numbers of positive and negative elements, the detecting relays ST will not be energized. In any other instance, i. e., whenever the signal is a mutilated one, relay ST is momentarily energized. This causes the armature 140 of said relay to be moved out of engagement with its back contact and into engagement with its front contact, such operation of the armature interrupts the supply of negative polarity through rotary timing contact 1%, in consequence of which no current is transmitted through the armatures 117-121, thereby preventing operation of the relays 114, 115 and 116, and also preventing the energization of conductor 125 leading to the correcting apparatus. This motion of the testing relay armature 140 also performs the additional function of applying negative polarity to conductor 52 which joins with conductor 125 and extends to the correcting apparatus.

Referring now to the details of this correcting apparatus illustrated in Figure 3, it will be seen that it comprises a multiplicity of rotary timing contacts 2tl12ii6 inclusive, which are mounted on the corrector timing shaft 218. This shaft 21% turns at one-sixth 4;) of speed of the transmitter distributor shaft. The aforementioned timing contacts 201206 on this shaft are opened and closed according to the timing diagram illustrated in Figure 7, in which time progresses from top to bottom. The left hand line in this diagram is divided into six parts, indicating six consecutive revolutions of the transmitter shafts.

The corrector shaft 218 normally stands inert, and is only set into motion upon the energization of start magnet 217. Whereupon this shaft is started and stopped in predetermined synchronous relation to the motion or" the transmitter distributor shaft, but only rotates at onesixth the speed of this latter shaft, as above mentioned. The start magnet 217 is energized whenever negative polarity is impressed upon conductors 125, 52. Thus, Whenever the receiving apparatus of Figure 2 receives warning signal VII, with the resulting energization of conductor 125, or whenever the receiving apparatus receives a signal which is mutilated, with the resulting energization of conductor 52, the start magnet 217 is energized, or is maintained in an energized condition, for either starting or maintaining the motion of the shaft 213.

The correcting appaatus also comprises a relay 213, the armatures or armature contacts of which are connected with negative polarity through conductor 23% which is controlled by rotary timing contact 2%1. The armature 220 of relay 213 receives this negative polarity from conductor 230 during the time that the shaft 218 is rotating. When the relay is deenergized, the armature 221) transmits this negative polarity through its back contact to the timing contact 294. it will be noted that this timing contact connects with conductor 144', which serves to energize the warning signal relay S2, for causing the emission of a warning signal from the transmitter.

However, so long as the correcting apparatus is inert, with the shaft 218 in its normal rest position, the timing contact 204 is open (see Figure 7), and hence conductor 144 is not energized. Upon the energization of selecting relay 213, movement of the armature 220 to its attracted position transmits negative polarity through a front contact to the rotary timing contact 206. In addition, the movement of the armature to this position transmits negative polarity over conductor 231 to the energized terminal of the relay winding 213 for locking up this relay until timing contact 201 interrupts the supply of negative polarity.

It will be noted that timing contact 206 is connected with conductor 143 which leads to the reverse or backstepping magnet T of the transmitter (Figure 1). Hence during the interval that the relay 213 is energized and the contact 266 is in its closed circuit position, negative polarity is transmitted over conductor 143 for causing backward movement of the perforated tape in the keyer. It will be noted from Figure 7 that the timing contact 206 has a span equal to approximately three revolutions of the transmitting distributor, and hence the perforated tape is stepped back three steps in each undisturbed or normal cycling of the correcting apparatus CA. As hereinafter described, the number of backward steps imparted to the perforated tape is reduced in situations of mutual disturbance between the two stations.

In order to clearly describe the action of the circuits of Figure 3, a preliminary discussion of Figure 8 is desirable, this figure showing the time elements concerned with the disturbed reception of a signal.

In this chart or time diagram the two left hand lines correspond to one station, such as station A, and the two right hand lines correspond to another station, such as station 13. Of the two left hand lines, line AT represents the transmitter and line AR represents the receiver of station A; and, similarly, of the two right hand lines, line BR represents the receiver and line BT represents the transmitter of station B. In these diagrams, time progresses from top to bottom. It has been supposed that the propagation time on the radio path amounts to about four signal elements, and that on both transmitters the alphabet is emitted (indicated by the letters a, b, 0 etc, A, B, C etc., respectively).

In Figure 8 the letter a is supposed to have been correctly received, but the letter b has been disturbed, this fact having given rise at the receiver BR to the operation of detecting relay ST, the energization of which relay applies a negative polarity to conductor 52, as previously described. The inclined dotted line in Figure 8 indicates the transmission of letter I), which has been disturbed or mutilated, and the solid continuation of this line indicates that the receiver BR warns its transmitter BT of the received disturbance. This warning is efiected by means of the correcting apparatus of Figure 3, which functions in such manner that the trans mitter BT transmits to the receiver AR one emission of warning signal VII.

The warning of the transmitter ET by its receiver BR is performed by the operation of testing relay ST at the receiver BR, by which relay contact is closed and working potential is applied to conductor 52. Referring to Figure 3, the application of working potential to conductor 52 results in the energization of the start magnet 217, which sets the shaft 218 into operation. Upon the starting of shaft 218, timing contact 201 and 204 are closed (Figure 7), and as a result, working potential is transmitted up through relay armature 220 and contact 204 to conductor 144 which extends up to warning signal relay S2. Hence, warning signal VII is emitted by the transmitter ET. This occurs during the first revolution of transmitter BT after the reception of a disturbance in receiver BR has been signalled.

It is to be observed that this signalling function does not occur before a time interval belonging to the element of the vertical line BR (Figure 8) following on that, in which this line intersects the inclined dotted line, is being traversed.

At timing contact 2112, the transmission of working potential to conductor 141 is interrupted during the time that the shaft 218 is rotating, the contact 202 being opened when the shaft starts rotating and not being closed until the shaft is again at rest.

Interrupting the supply of working potential to the conductor 141 prevents the printer from starting or operating during the time that the shaft 218 is rotating.

The opening of contact 203 at this same time interrupts the supply of working potential to conductor 142 so that the supply circuit for the start or advancing mag- 13, net S is deenergized at the same time that the supply circuit for the printer is.deenergized.

By reason of the abovedescribed closing of timing contact 204; warning signal. VII is. emitted: once, this occurring during; that. part. of the. motion: of shaft 218. corre sponding to. the, first revolution of the: transmitting distributor (Figure, 7),.

Figure 8, illustrates. the emission of the warning signal VII from the transmitter BT, and the reception of this warning signal at receiver AR.

I shall now explain what action this warning signal has on the receiver AR and the transmitter AT. The reception of this warning signal on receiver AR operates through relays 111-113 and armatures 117-121 to apply working potential to the conductor 125 which leads to the correcting apparatus of station A. As shown in Figure 3, the energization of conductor 125 energizes start magnet 217 and starts the operation of Corrector.

shaft 218 of station A. At the same time that start magnet 217 is energized over conductor 125 selecting relay 213 is also energized. The energization of relay 213 causes the transmitter AT to first make three steps in a backward direction and then three steps in a forward direction. Referring again to Figure 8, the above described operation of stepping transmitter AT in a backward direction through three steps, and then in a forward direction through three steps, results in the repetition of the signal which has been received in a dis turbed condition. That is to say, the letter b is again emitted on the 6th step after that in which the mutilated letter had been emitted. The manner in which the correcting apparatus of Figure 3 controls the automatic keyer to make the required steps after the application of working voltage to lead 125 will now be described. On the application of negative potential to lead 125, relay 213 and start magnet 217 are energized. The relay actuates its armature 220, and the start magnet starts the shaft 218. By the actuation of armaure 220, working potenial is taken from conductors 144 and 145, and this potential is applied by way of contact 206 to conductor 143. This conductor energizes the reverse or backward stepping magnet T, which steps back the keyer when energized. The contact 206 is closed during three revolutions of the transmitter shaft, and hence the automatic keyer is stepped back over three steps.

Thereafter the forward advance magnet S is energized and advances the keyer by three steps.

In all other cases of mutual and/or simultaneous disturbance than those examined more in detail, the circuit described yields the correct results as may be easily concluded by referring to the examples given. Synchronism between transmitter shaft A and receiver shaft B, as well as between transmitter shaft B and receiver shaft A, is maintained in a known manner.

While I have illustrated and described what I regard to be the preferred embodiment of my invention, nevertheless it will be understood that such is merely exemplary and that numerous modifications and rearrangements may be made therein with out departing from the essence of the invention.

I claim:

1. In a radio telegraph system, in combination a plurality of stations interconnected by a common communication link, said station comprising a radio transmitter and a radio receiver, signalling means in each transmitter for formulating signals in a code of elements of a different nature in which said elements of a different nature occur in a mutually constant ratio in each signal, each receiver comprising testing means for testing each received signal to determine if said elements of different nature in that signal are in said mutually constant ratio, corrector apparatus at each station for responding to the testing device of that station when the latter indicates the reception of a signal which has been mutilated during the transmission, said correcting apparatus including means operative in a single cycle to effect the blocking of the associated receiver for a predetermined signal interval, the transmission of a single warning signal over said link and the setback of the associated transmitter a predetermined number of steps, whereby the retransmission of the portion of the signal which has been mutilated may be accurately effected, and warning signal detecting means in each receiver connected to said corrector appartus means to control said corrector apparatus in the manner of said testing means responsive to receipt of said given 14 signal; warning; signal; from; the remote station, whereby. with mutilation of" both: an element of a message, and the consequent warning signal, retransmission or the message from the point of interruption is effected with.- out additional delay:

2. A radio telegraph system as set forth in claim. 1 in which the corrector apparatus is; cycled once with eachoperation of said testing means. and said warning signal detection means to control its associated transmitter. to terminate its signal transmission and to be setback a predetermined number of steps which is commensurate with the time for propagation of the signals over said radio link and which includes means for initiating immediate repetition of the message following accomplishment of said given setback.

3. A telegraph system as set forth in claim 1 in which each of said stations includes a signal printer for recording received messages and in which said corrective apparatus is operative at each of said stations to stop said printer on receipt of said single warning signal and to maintain said printer stopped for a period time sufficient in length to maintain the receiver of the station in a blocked condition with the receipt of the warning signal transmitted by the other station responsive to receipt of a mutilated ordinary signal, a mutilated warning signal or an unmutilated warning signal thereby.

4. In a radio telegraph system comprising a plurality of stations connected by a common communication link, each of said stations comprising a transmitter having a transmitter distributor for transmitting signals of a predetermined length, each signal having a plurality of elements in a predetermined fixed ratio, a receiver including testing means for testing each received signal to determine if said plurality of elements is present in said mutual constant ratio, warning signal detecting means for responding only to a given one of said signals, correcting apparatus at each station including circuit control means for causing the transmitter of that station to transmit a single warning signal and for causing said transmitter to back up to effect retransmission of a given portion of the message, and timing means in each corrector apparatus for blocking the receiver at each station for a predetermined period of time which is no longer than the time duration of six of said signals in any given operation initiated responsive to mutilation of a single message signal and the mutilation of the warning signal returned as a result thereof, and common energizing means controlled by said testing means and said Warning signal detection means for energizing said correcting apparatus for one cycle with each operation of one of said last two means.

5. An arrangement as set forth in claim 4 in which said correcting apparatus comprises a time control shaft and relay means operated responsive to each energization of said common control means to cause said time control shaft to rotate at a speed one-sixth of that of said transmitter distributor, and a first timing contact on said control shaft for controlling the transmitter at the associated station to effect the transmission of a single warning over the communication link, a second timing contact for setting back the signal transmitter means a given number of steps commensurate with the radio propagation time of the signals, and a third timing contact for effecting operation of the transmitter equipment to effect the retransmission of certain portions of the messages.

6. In a radio telegraph system the combination of a radio transmitter comprising means for establishing signals characterized by a fixed ratio of positive and negative impulses in each signal, means for transmitting such signals over an associated communication link in such manner that the components of the signal are representative of the same fixed ratio of said positive and negative impulses, radio receiver means associated with said radio transmitter comprising means for converting the components of radio signals of the above type back into corresponding positive and negative impulses, printer means for printing said converted signal; said receiver means including test means operative to test said converted signals for said fixed ratio of positive and negative impulses and warning signal detecting means for responding only to a single predetermined warning signal received from the remote station; and corrector apparatus connected with said radio receiver and said radio transmitter at each of the stations to be cycled once by said testing means and said warning signal detecting means with each operation thereof; said corrector apparatus comprising control means operative with energization of said corrector means i References Cited in the file of this ,patent to 'efiFect retransmission of the portion'of the message I afiected by said mutilactlion, printar circuitfcontrol means UNITED STATES PATENTS 0 erative to prevent sai associate printer rom operating f r a given period of a length less than the length of six 5 %i ig f f 2 %8 of said signals, and transmitter starting means for causing 205O265 B0311 1942 said transmitter to send only a single warning signal in its 2279353 van aggfl A 1942 cycle, whereby with the mutilation of an element in a 2313980 Van Duuren g 1943 message transmission and the mutilation of the returned warning signal a delay period of less than six signal lengths 10 is experienced. 

